1. Field of the Invention
The present invention relates to a printing apparatus that prints an image on a print medium by using a print head capable of ejecting ink from a plurality of nozzles and also to an image processing apparatus that sends print data to the printing apparatus.
2. Description of the Related Art
Generally, a printing apparatus using an ink ejecting print head may not be able to perform the normal printing operation when the number of ink ejections from the nozzles of the print head exceeds a predetermined value.
Among the ink jet print heads there is a thermal ink jet print head which has electrothermal transducers (heaters) as a means to generate ink ejection energy. This type of print head quickly heats ink by the electrothermal transducer to create a bubble in the ink and expels an ink droplet from the nozzle by a pressure of the expanding bubble. Such a thermal ink jet print head is subjected to stresses, such as heat, pressure and chemical reactions with ink, over a long period of use in the ink jet printing apparatus. These stresses increase the resistance of the heater, causing an excess heating of the heater and therefore a burning of the ink. This in turn will lead to a reduced volume of ink ejected, resulting in the print head failing to eject ink properly, degrading a quality of printed image.
A conventional practice to prevent this from happening, for example, involves counting the number of ink ejections from the print head and, when the count value reaches a predetermined value, notifying the user that the print head has reached the end of its life. More specifically, a plurality of nozzles of the print head is divided into nozzle blocks and, each time one page is printed, the total number of ink ejections in every block is monitored. The total number of ejections in each block is the total number of ink droplets ejected from the nozzles in that block and equals the total number of dots (printed dots) formed by the ejected ink droplets. The total number of dots in each block is counted by a host computer (or host device) and the count value is sent to the printing apparatus as dot count data. The printing apparatus totals the dot count data for each nozzle block of the print head as the number of printed pages increases. In this manner, the total ink droplets ejected from each nozzle block of the print head is managed and, when the total count value reaches a specified value, it is decided that the print head has reached the end of its longevity.
The above conventional method, however, has the following problems.
(1) The dot count data needs to be processed for each printed page. Thus, the host computer has a heavy burden of counting the dots to make the dot count data and the printing apparatus is burdened heavily by the processing of adding up the dot count data. As a result, throughput inevitably degrades.
(2) In addition to the print data the host computer must send the dot count data for each print page to the printing apparatus. This lowers the print data transfer rate.
(3) The dot count data is preferably managed for each nozzle. But in reality the dot count data is managed for each group of multiple nozzles (for each nozzle block) as described in (1) and (2), so the accuracy of the dot count data as management data on the print head serviceable life degrades. For example, when the dot count data is managed for each 10 nozzles, a distinction cannot be made between a case where ink is ejected uniformly from all 10 nozzles and a case where a frequency of ink ejection from a particular nozzle is extremely high. In this situation, an error of up to 10 times can occur. Particularly, in a printing apparatus using an elongate print head extending over the entire printing width of a print medium (line head), if a line which is one dot thick is to be printed, the number of ink ejections from a particular nozzle becomes extremely large, making the above problem conspicuous.